Because many LCD devices have the advantages of portability, low power consumption, and low radiation, they have been widely used in various portable information products such as notebooks, personal digital assistants (PDAs), video cameras, and the like. Furthermore, LCD devices are considered by many to have the potential to completely replace cathode ray tube (CRT) monitors and televisions.
Referring to FIG. 4, a typical LCD 10 includes a liquid crystal panel 11, a timing controller 12, a gate driving circuit 13, a data driving circuit 14, and a common voltage source 15. The gate driving circuit 13 is used for providing a plurality of scanning signals to the liquid crystal panel 11. The data driving circuit 14 is used for providing a plurality of gray scale voltages to the liquid crystal panel 11. The timing controller 12 is used for controlling the gate driving circuit 13 and the data driving circuit 14. The common voltage source 15 is used for providing a predetermined common voltage to the liquid crystal panel 11.
The liquid crystal panel 11 includes a plurality of scanning lines 131 parallel to each other, a plurality of data lines 141 parallel to each other and orthogonal to the scanning lines 131, a common voltage line 101, a plurality of thin film transistors (TFTs) 16 arranged in the vicinity of points of intersection of the scanning lines 131 and the data lines 141, a plurality of pixel electrodes 17 corresponding to the TFTs 16, and a plurality of common electrodes 18 generally opposite to the pixel electrodes 17 respectively.
Each TFT 16 includes a gate electrode (not labeled) connected to the corresponding scanning line 131, a source electrode (not labeled) connected to the corresponding data line 141, and a drain electrode (not labeled) connected to the pixel electrode 17. The common electrodes 18 of the TFTs 16 are substantially connected together and to the common voltage source 15 via the common voltage line 101. The common voltage line 101 is insulated from the scanning lines 131 and the data lines 141, and is arranged at an edge of the liquid crystal panel 11 near the gate driving circuit 13. A plurality of branch lines (not labeled) extend from the common voltage line 101, each branch line connecting to a respective row of the common electrodes 18. Thereby, all the common electrodes 18 have the common voltage applied thereto. The common voltage is a constant direct current voltage, and may for example be 5 volts (V).
The timing controller 12 generates a plurality of scanning synchronization signals (S-SYNC), and provides the S-SYNC to the gate driving circuit 13. The gate driving circuit 13 thereby applies plural scanning signals to the scanning lines 131 sequentially. When one scanning line 131 is being scanned, the corresponding TFTs 16 that are connected to the scanning line 131 are switched on.
The timing controller 12 further generates a plurality of data synchronization signals (D-SYNC), and provides the D-SYNC to the data driving circuit 14. The data driving circuit 14 thereby applies plural gray scale voltages to the data lines 141 simultaneously each time one of the scanning lines 131 is being scanned. The gray scale voltages are applied to corresponding pixel electrodes 17 via corresponding on-state TFTs 16.
When a gray scale voltage is applied to each pixel electrode 17, an electric field is generated between the pixel electrode 17 and the corresponding common electrode 18. Generally, the scanning lines 131 and the data lines 141 are insulated from each other by an insulating layer provided therebetween. Therefore, parasitic capacitors are inevitably formed between the scanning lines 131 and the data lines 141. Each parasitic capacitor is capable of interfering with operation of the liquid crystal panel 11. In particular, when the gray scale voltages applied to the pixel electrode 17 are pulled up or pulled down rapidly, the voltage of the common electrode 18 corresponding to the pixel electrode 17 is correspondingly pulled up or pulled down due to a coupling effect of the parasitic capacitor. When this happens, the voltages of other common electrodes 18 are distorted correspondingly, and so-called ripples in voltages of other common electrodes 18 occurs. These disturbances are liable to impair the quality of images displayed by the LCD 10. Further, these disturbances are liable to induce crosstalk, which can degrade operation of the liquid crystal panel 11 and further impair the quality of images displayed by the LCD 10.
What is needed, therefore, is an LCD that can overcome the above-described deficiencies.